A primary application of the invention disclosed herein is for use as an automobile fuel sensor. Automobile fuel gauges are notoriously inaccurate, indicating that the tank is empty when there are several gallons of fuel left and remaining on full for the first 50 miles after filling the tank. They are also prone to mechanical malfunction associated with sticking of the moving parts of the gauge
This commonly employed prior art fuel sensor, also known as the fuel sensing unit, is located in the fuel tank and consists of a float connected to a metal rod. The end of the rod is mounted to the “wiper” of a variable resistor. The variable resistor consists of a strip of resistive material connected on one side to the ground. The wiper, which is also connected to the dashboard fuel gauge, slides along the strip of resistive material as the fuel level in the tank changes. In accordance with Ohm's Law, the more resistance there is, the less current will flow and the less resistance there is, the more current will flow. The amount of fuel in the tank correlates with the current flowing through the resistor and fuel gauge. When the tank is full, the float is at the top of the tank and the wiper is near the grounded side of the strip. Therefore, there is little or no resistive material in the path of the current and the current flow is at a maximum. As the fuel level in the tank drops, the float sinks, the wiper moves, the resistance increases and the amount of current flowing through the gauge decreases. When the tank is empty the float is at the bottom of the tank and the wiper is at the far end of the strip. Thus, there is more resistive material in the in the path of the current, and the current flow is at a minimum.
The mechanical float is a primary reason for the inaccuracy of fuel gauges. It is common for fuel gauges to remain on full for quite a while after filling the tank. When the tank is full, the float is at its maximum raised position which is dictated by the connecting rod and/or the top of the tank. This results in the float being submerged, and the float will not drop until the fuel level drops to a position near the bottom of the float. Therefore, the fuel gauge indicator won't start to move until the float starts to drop.
Similar inaccuracies are introduced when the float nears the bottom of the tank. Typically, the range of motion does not extend to the very bottom of the tank and the float can reach the bottom of its travel while there is still fuel in the tank. As a result, the fuel gauge indicates that the tank is empty while there are still several gallons of fuel left in the tank.
In addition, the shape of the fuel tanks themselves can also introduce inaccuracies. Today's fuel tanks are made from plastics, molded to fit into very tight spaces. Fuel tanks are typically shaped to fit around components of the cars body or frame. This means that when the float reaches the halfway point on the tank, there may be more or less than half of the fuel left in the tank, depending on its shape.
Thus, there is a need for a liquid level sensor for replacing the cumbersome inaccurate float apparatus with a sensor that accurately indicates the volume of liquid such as fuel in the fuel tanks and including various vehicles that have widely varying fuel tank shapes and to do so with a liquid level sensor having a much lower manufacturing cost than the aforesaid float apparatus.
Also, in contrast with the manufacture of such discrete probes of limited length, it would also be desirable to provide rolls of long hydrostatic liquid sensor elements that can be cut into customized length sections from the rolls to form sensors to be positioned down deep liquid storage tanks or even deeper groundwater wells for example, without the need to join shorter discrete probes together. The use of such rolls enables on the spot variations of lengths of sensors for immediately fabricating various customized sensors. For example, a tank farm may have tanks of liquid having many various depths and it would be desirable to rapidly and easily provide sensors of varying length under these circumstances.